USJ techniques with helium-treated substrates

ABSTRACT

A method of using helium to create ultra shallow junctions is disclosed. A pre-implantation amorphization using helium has significant advantages. For example, it has been shown that dopants will penetrate the substrate only to the amorphous-crystalline interface, and no further. Therefore, by properly determining the implant energy of helium, it is possible to exactly determine the junction depth. Increased doses of dopant simply reduce the substrate resistance with no effect on junction depth. Furthermore, the lateral straggle of helium is related to the implant energy and the dose rate of the helium PAI, therefore lateral diffusion can also be determined based on the implant energy and dose rate of the helium PAI. Thus, dopant may be precisely implanted beneath a sidewall spacer, or other obstruction.

This application claims priority of U.S. Provisional Patent ApplicationNo. 61/088,809, filed on Aug. 14, 2008, the disclosure of which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

Ion implanters are commonly used in the production of semiconductorwafers. An ion source is used to create a beam of charged ions, which isthen directed toward the wafer. As the ions strike the wafer, theyimpart a charge in the area of impact. This charge allows thatparticular region of the wafer to be properly “doped”. The configurationof doped regions defines their functionality, and through the use ofconductive interconnects, these wafers can be transformed into complexcircuits.

FIG. 1 is a block diagram of a plasma doping system 100, while FIG. 2 isa block diagram of a beam-line ion implanter 200. Those skilled in theart will recognize that the plasma doping system 100 and the beam-lineion implanter 200 are each only one of many examples of differing plasmadoping systems and beam-line ion implanters that can provide ions. Thisprocess also may be performed with other ion implantation systems orother substrate or semiconductor wafer processing equipment. While asilicon substrate is discussed in many embodiments, this process alsomay be applied to substrates composed of SiC, GaN, GaP, GaAs,polysilicon, Ge, quartz, or other materials known to those skilled inthe art.

Turning to FIG. 1, the plasma doping system 100 includes a processchamber 102 defining an enclosed volume 103. A platen 134 may bepositioned in the process chamber 102 to support a substrate 138. In oneinstance, the substrate 138 may be a semiconductor wafer having a diskshape, such as, in one embodiment, a 300 millimeter (mm) diametersilicon wafer. The substrate 138 may be clamped to a flat surface of theplaten 134 by electrostatic or mechanical forces. In one embodiment, theplaten 134 may include conductive pins (not shown) for making connectionto the substrate 138.

A gas source 104 provides a dopant gas to the interior volume 103 of theprocess chamber 102 through the mass flow controller 106. A gas baffle170 is positioned in the process chamber 102 to deflect the flow of gasfrom the gas source 104. A pressure gauge 108 measures the pressureinside the process chamber 102. A vacuum pump 112 evacuates exhaustsfrom the process chamber 102 through an exhaust port 110 in the processchamber 102. An exhaust valve 114 controls the exhaust conductancethrough the exhaust port 110.

The plasma doping system 100 may further include a gas pressurecontroller 116 that is electrically connected to the mass flowcontroller 106, the pressure gauge 108, and the exhaust valve 114. Thegas pressure controller 116 may be configured to maintain a desiredpressure in the process chamber 102 by controlling either the exhaustconductance with the exhaust valve 114 or a process gas flow rate withthe mass flow controller 106 in a feedback loop that is responsive tothe pressure gauge 108.

The process chamber 102 may have a chamber top 118 that includes a firstsection 120 formed of a dielectric material that extends in a generallyhorizontal direction. The chamber top 118 also includes a second section122 formed of a dielectric material that extends a height from the firstsection 120 in a generally vertical direction. The chamber top 118further includes a lid 124 formed of an electrically and thermallyconductive material that extends across the second section 122 in ahorizontal direction.

The plasma doping system may further include a source 101 configured togenerate a plasma 140 within the process chamber 102. The source 101 mayinclude a RF source 150, such as a power supply, to supply RF power toeither one or both of the planar antenna 126 and the helical antenna 146to generate the plasma 140. The RF source 150 may be coupled to theantennas 126, 146 by an impedance matching network 152 that matches theoutput impedance of the RF source 150 to the impedance of the RFantennas 126, 146 in order to maximize the power transferred from the RFsource 150 to the RF antennas 126, 146.

The plasma doping system 100 also may include a bias power supply 148electrically coupled to the platen 134. The bias power supply 148 isconfigured to provide a pulsed platen signal having pulse on and offtime periods to bias the platen 134, and, hence, the substrate 138, andto accelerate ions from the plasma 140 toward the substrate 138 duringthe pulse on time periods and not during the pulse off periods. The biaspower supply 148 may be a DC or an RF power supply.

The plasma doping system 100 may further include a shield ring 194disposed around the platen 134. As is known in the art, the shield ring194 may be biased to improve the uniformity of implanted iondistribution near the edge of the substrate 138. One or more Faradaysensors such as an annular Faraday sensor 199 may be positioned in theshield ring 194 to sense ion beam current.

The plasma doping system 100 may further include a controller 156 and auser interface system 158. The controller 156 can be or include ageneral-purpose computer or network of general-purpose computers thatmay be programmed to perform desired input/output functions. Thecontroller 156 can also include other electronic circuitry orcomponents, such as application-specific integrated circuits, otherhardwired or programmable electronic devices, discrete element circuits,etc. The controller 156 also may include communication devices, datastorage devices, and software. For clarity of illustration, thecontroller 156 is illustrated as providing only an output signal to thepower supplies 148, 150, and receiving input signals from the Faradaysensor 199. Those skilled in the art will recognize that the controller156 may provide output signals to other components of the plasma dopingsystem and receive input signals from the same. The user interfacesystem 158 may include devices such as touch screens, keyboards, userpointing devices, displays, printers, etc. to allow a user to inputcommands and/or data and/or to monitor the plasma doping system via thecontroller 156.

In operation, the gas source 104 supplies a primary dopant gascontaining a desired dopant for implantation into the substrate 138. Thegas pressure controller 116 regulates the rate at which the primarydopant gas is supplied to the process chamber 102. The source 101 isconfigured to generate the plasma 140 within the process chamber 102.The source 101 may be controlled by the controller 156. To generate theplasma 140, the RF source 150 resonates RF currents in at least one ofthe RF antennas 126, 146 to produce an oscillating magnetic field. Theoscillating magnetic field induces RF currents into the process chamber102. The RF currents in the process chamber 102 excite and ionize theprimary dopant gas to generate the plasma 140.

The bias power supply 148 provides a pulsed platen signal to bias theplaten 134 and, hence, the substrate 138 to accelerate ions from theplasma 140 toward the substrate 138 during the pulse on periods of thepulsed platen signal. The frequency of the pulsed platen signal and/orthe duty cycle of the pulses may be selected to provide a desired doserate. The amplitude of the pulsed platen signal may be selected toprovide a desired energy. With all other parameters being equal, agreater energy will result in a greater implanted depth. The plasmadoping system 100 may incorporate hot or cold implantation of ions insome embodiments.

Turning to FIG. 2, a beam-line ion implanter 200 may produce ions fortreating a selected substrate. In one instance, this may be for doping asemiconductor wafer. In general, the beam-line ion implanter 200includes an ion source 280 to generate ions that form an ion beam 281.The ion source 280 may include an ion chamber 283 and a gas boxcontaining a gas to be ionized. The gas is supplied to the ion chamber283 where the gas is ionized. This gas may be or may include or contain,in some embodiments, hydrogen, helium, other rare gases, oxygen,nitrogen, arsenic, boron, phosphorus, carborane, alkanes, or anotherlarge molecular compound. The ions thus generated are extracted from theion chamber 283 to form the ion beam 281. A power supply is connected toan extraction electrode of the ion source 280 and provides an adjustablevoltage.

The ion beam 281 passes through a suppression electrode 284 and groundelectrode 285 to mass analyzer 286. Mass analyzer 286 includes resolvingmagnet 282 and masking electrode 288 having resolving aperture 289.Resolving magnet 282 deflects ions in the ion beam 281 such that ions ofa desired ion species pass through the resolving aperture 289. Undesiredion species do not pass through the resolving aperture 289, but areblocked by the masking electrode 288.

Ions of the desired ion species pass through the resolving aperture 289to the angle corrector magnet 294. Angle corrector magnet 294 deflectsions of the desired ion species and converts the ion beam from adiverging ion beam to ribbon ion beam 212, which has substantiallyparallel ion trajectories. The beam-line ion implanter 200 may furtherinclude acceleration or deceleration units in some embodiments.

An end station 211 supports one or more substrates, such as substrate138, in the path of ribbon ion beam 212 such that ions of the desiredspecies are implanted into substrate 138. The substrate 138 may be, forexample, a silicon wafer or a solar panel. The end station 211 mayinclude a platen 295 to support the substrate 138. The end station 211also may include a scanner (not shown) for moving the substrate 138perpendicular to the long dimension of the ribbon ion beam 212cross-section, thereby distributing ions over the entire surface ofsubstrate 138. Although the ribbon ion beam 212 is illustrated, otherembodiments may provide a spot beam.

The ion implanter 200 may include additional components known to thoseskilled in the art. For example, the end station 211 typically includesautomated substrate handling equipment for introducing substrates intothe beam-line ion implanter 200 and for removing substrates after ionimplantation. The end station 211 also may include a dose measuringsystem, an electron flood gun, or other known components. It will beunderstood to those skilled in the art that the entire path traversed bythe ion beam is evacuated during ion implantation. The beam-line ionimplanter 200 may incorporate hot or cold implantation of ions in someembodiments.

As stated above, ion implantation is a standard technique forintroducing conductivity-altering impurities into semiconductorsubstrates. A desired impurity material is ionized in an ion source, theions are accelerated, and the ions are directed at the surface of thesubstrate. The energetic ions penetrate into the bulk of thesemiconductor material. Following an annealing process, the ions maybecome incorporated into the crystalline lattice of the semiconductormaterial to form a region of desired conductivity.

Silicon or other materials may also have an amorphous crystal structure.In a silicon substrate, one silicon atom is usually tetrahedrally bondedto four neighboring silicon atoms and these silicon atoms will form awell-ordered lattice across the substrate. In contrast, this order doesnot exist in amorphous silicon. Instead, the silicon atoms form a randomnetwork and the silicon atoms may not be tetrahedrally bonded to fourother silicon atoms. In fact, some silicon atoms may have danglingbonds.

Amorphizing implants, such as a pre-amorphizing implant (PAI), are usedto amorphize the crystal lattice of a substrate. Prior to theamorphizing implant, the substrate usually has a crystal lattice with along-range order. Such a structure allows implanted ions to move throughthe crystal, or channel. By amorphizing the substrate, channeling ofdopants, or implantation of ions substantially between the crystallattice of the substrate, during later implantation may be prevented orreduced because the substrate will lack a long-range order. Thus, thedopant implant profile may be kept shallow.

Previously, USJ formation had been performed with a PAI using heavierspecies such as germanium and silicon to prevent channeling. This methodmay cause residual damage at the end of range and subsequent leakage incomplementary metal oxide semiconductor (CMOS) transistors. Yet, if thePAI step was removed, channeling of ions will occur, thereby increasingthe junction depths. Additionally, advances in USJ have requiredannealing technologies capable of millisecond (MS) thermal budgets neara target temperature. A MS anneal is unable to completely remove implantdamage caused by silicon or germanium PAI, and specifically end of range(EOR) defects. Furthermore, there is a lack of lateral diffusion of adopant in the substrate. This lack of lateral diffusion may causeoverlap capacitance issues within a device.

Accordingly, there is a need to improve the implantation methods used toform USJ and, more particularly, there is a need to create methods usinghelium to form ultra shallow junctions.

SUMMARY OF THE INVENTION

The problems of the prior art are addressed by the present disclosure,which describes a method of using helium to create ultra shallowjunctions. A pre-implantation amorphization using helium has significantadvantages. For example, it has been shown that upon anneal dopants willpenetrate the substrate only to the original amorphous-crystallineinterface, and no further. Therefore, by properly determining theimplant energy of helium, it is possible to exactly determine thejunction depth. Increased doses of dopant enhance the activation therebylowering the substrate resistance without affecting junction depth.Furthermore, the lateral straggle of helium is related to the implantenergy and the dose rate of the helium PAI, therefore lateral diffusioncan also be determined based on the implant energy and dose rate of thehelium PAI. Thus, dopant may be precisely implanted beneath a sidewallspacer, or other obstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present disclosure, reference is madeto the accompanying drawings, in which like elements are referenced withlike numerals, and in which:

FIG. 1 is a block diagram of a plasma doping system;

FIG. 2 is a block diagram of a beam-line ion implanter;

FIG. 3 is a substrate with an amorphous crystal structure caused by aPAI;

FIGS. 4A-4C are cross-sectional views of actual versus target profiles;

FIG. 5 is a cross-sectional view of the amorphous-crystalline interface;

FIG. 6 is a cross-sectional view of boron diffusion;

FIG. 7 is a cross-sectional view of a lack of lateral diffusion;

FIGS. 8A-8C illustrate lateral straggle control;

FIGS. 9A-9E illustrate lateral straggle control;

FIGS. 10A-10D are cross-sectional views of improving lateral straggle;and

FIGS. 11A-11B illustrate junction depth using helium PAI.

DETAILED DESCRIPTION OF THE INVENTION

As stated above, silicon is typically a crystalline structure, whereeach silicon atom is tetrahedrally bonded to four neighboring siliconatoms. By bombarding this crystalline structure with atoms, such assilicon, germanium, or helium, the crystalline structure of the siliconworkpiece can be altered. FIG. 3 is a substrate with an amorphouscrystal structure. This crystal lattice 300 is implanted with ions 301to cause this amorphous structure. This crystal lattice 300 which may bemade up of, for example, silicon atoms, is amorphous, lacks a long-rangeorder, and includes some atoms with dangling bonds. These ions 301 maybe part of a helium PAI, for example. Since the crystal lattice 300lacks a long-range order, the channels within the crystal lattice 300 donot exist. Thus, ions are unable to channel between the crystal lattice300.

By bombarding ion to amorphize the substrate, channeling of implantedions can be eliminated. However, while PAI eliminates the channelingissue, it causes other problems. The implantation of ions, specificallyheavier species such as germanium and silicon, causes residual damage atend of range (EOR). The end of range is the lowest depth within thesubstrate where implanted ions reach. These EOR defects cause subsequentleakage in the CMOS transistors. Ultra shallow junctions also requireannealing techniques capable of millisecond (MS) thermal budgets nearthe target temperature. Two drawbacks in the MS only anneal are theinability to completely remove the implant damage, specifically EORdefects described above, and the lack of lateral diffusion of thedopant, which causes overlap capacitance issues within the device.

A helium PAI solves the problems of preventing channeling of ions andenabling a MS anneal. As is the case with other implants, a helium PAIhas the ability to amorphize a substrate so that channeling of ions isprevented. In addition, it has been found that a helium PAI also resultsin no residual damage after annealing. Additionally, during the annealprocess after a helium PAI, some implanted dopant ions, such as boron,carborane, arsenic, phosphorus and others, will transport to theoriginal amorphous-crystalline interface that was created by the heliumPAI. Tests have shown that these implanted ions do not diffuse past theoriginal amorphous-crystalline interface, rather they stop at thatinterface. This transport phenomenon gives helium the ability to tailorjunction depth (x_(j)) and/or lateral diffusion. A helium PAI may, thus,enable an MS anneal by overcoming issues associated with lateraldiffusion. The helium PAI also may enable an MS anneal or tailoring ofjunction depth for other dopants besides boron, such as arsenic orphosphorus. A helium PAI also will fully repair with a solid phaseepitaxy (SPE) anneal or MS anneal whereas a germanium or silicon PAIwill not. Furthermore, because there is no residual damage, a helium PAIalso will not cause substantial leakage, unlike a germanium PAI.

As mentioned above, use of an MS anneal without a rapid thermalprocessing (RTP) step for germanium or silicon PAI has two main issues.First, there is an inability to fully repair implant damage, which maylead to device leakage. Second, there is a lack of lateral diffusion.Lateral diffusion is the diffusion of a dopant, such as boron, from theimplanted region to the target profile after anneal. This isproblematic; especially in the region beneath the sidewall spacers.FIGS. 4A-4C are cross-sectional views of actual profiles versus targetprofiles. FIG. 4C shows the target profile 401, where boron is implantedbeneath the sidewalls 402. FIG. 4A shows the actual implanted region 400following a MS anneal. The lack of lateral diffusion keeps the actualprofile 400 from achieving the target profile 401, leaving a gap betweenthe gate and the implanted region, as shown in FIG. 4B. This may lead tooverlap capacitance issues or undesired channel conductance.

FIGS. 11A-11B show several important characteristics of helium PAI. InFIG. 11A, the dose rate of the helium is varied, while the Rs is keptconstant. The graph shows that by varying the helium dose rate, apredefined junction depth can be achieved for a specific substrateresistance. Higher dose rates result in shallower junction depths.

FIG. 11B shows the effects of increased dopant dose on a substrate whichhas undergone helium PAI. Note that in this case, the dose of aparticular dopant does not affect the junction depth, rather only the Rsis changed. In other words, increasing doses of dopant retain the samejunction depth, but with a reduction in substrate resistance. In allcases, a fixed helium PAI of a predetermined dose rate and implantenergy was performed. Following that, ion implants of BF₂ and carboranewere performed at various doses, and the resulting junction depths weremeasured. Note that in the case of carborane, the increased dose doesnot increase the junction depth beyond about 13 nm. While the graphshows an increase in junction depth resulting from an increased dose ofBF₂, it is believed that the dopant has not yet reached theamorphous-crystalline interface. Further increases in the dose of BF2would show similar results to those demonstrates by carborane. Thus,junction depth can be determined by proper dose rate during the heliumPAI.

FIG. 5 is a cross-sectional view of semiconductor substrate following ahelium PAI. The depth of the helium atoms defines theamorphous-crystalline interface 500. As shown in FIG. 11B, subsequentimplants will diffuse only to the amorphous-crystalline interface, andno further. In other words, the dopants will diffuse through theamorphous region, but may not diffuse into the crystalline region. Thus,the shape and depth of the dopant profile may be tailored by the properapplication of the helium PAI. In some embodiments, the implant energyof the helium PAI is varied to determine the thickness of the amorphouslayer. In a plasma processing system, implant energy is controlled bythe magnitude of the bias voltage applied to the platen. In a beamlinesystem, implant energy can be controlled by the voltage applied to theelectrodes 284, 285. In another embodiment, the thickness of theamorphous layer may be controlled by using a constant energy during thePAI implant. For example, as shown in FIG. 11A, the dose rate of thehelium PAI can control the depth of amorphous layer. In a plasmaprocessing system, the dose rate can be changed by varying the RF poweras controlled by antenna 126, 146, implant pressure, the duty cycle ofthe platen bias voltage, or He flow. In a beam line system, dose ratecan be varied by varying the extracted ion beam current, or by modifyingthe size or shape of the ion beam.

FIG. 6 is a cross-sectional view of a substrate following a borondiffusion occurring after a helium PAI. If boron is implanted in onlythe implanted region 600, the boron will diffuse throughout theamorphized region caused by a PAI implant that is within theamorphous-crystalline interface (represented by the dotted line 601 inFIG. 6). The boron will not substantially diffuse past theamorphous-crystalline interface. In one particular embodiment, thehelium PAI is implanted at 250V in the plasma doping system 100,although other bias voltages or implantation methods are possible.

Notice that the helium PAI shown in FIGS. 5 and 6 create anamorphous-crystalline interface that is located beneath the sidewallspacer 700. However, this amorphous-crystalline interface does notextend to the gate. FIG. 7 is a cross-sectional view of thesemiconductor device, which demonstrates this lack of lateral diffusion.This lack of lateral diffusion may lead to overlap capacitance, as shownin FIG. 4. Since the dopant cannot diffuse past theamorphous-crystalline interface, improper placement of anamorphous-crystalline interface may at least partly cause this lack oflateral diffusion. To avoid overlap capacitance, the implanted dopant701 needs to diffuse fully under the sidewall spacer 700. In order forthis to occur, the amorphous-crystalline interface must be located nearthe gate.

One factor that affects the location of the amorphous-crystallineinterface in FIGS. 5-7 is the lateral straggle of helium during the PAIprocess. Lateral straggle is defined as the motion of ions parallel tothe wafer as a result of ion implantation. In other words, more lateralmovement (or straggle) would create an amorphous-crystalline interfacethat extends further beneath the sidewall spacer.

FIGS. 8A-8C illustrate the use of implant voltage to control lateralstraggle. Use of an atom with a light atomic weight, such as helium, andvaried implant energy allows control of this lateral straggle. Controlof lateral straggle allows control of lateral amorphization and,therefore, dopant lateral diffusion. FIGS. 8A-8C illustrate the effectof increased implant energy. In all cases, a helium PAI was performedusing a plasma doping system 100, as shown in FIG. 1, followed by aboron ion implantation. FIG. 8A shows the profile of dopant within thesubstrate when the helium implanted at a voltage of 250V. Note that thediffusion profile has a depth of roughly 150 Å, while the implanted ionshave a lateral straggle of about 200 Å. Increasing the voltage appliedto the platen to 500V during PAI, as shown in FIG. 8B, creates a largerdiffusion profile, about 200 Å in depth and 300 Å in the lateraldirection. Finally, applying a voltage of about 1000V to the platenduring the helium PAI creates a diffusion profile having a depth ofabout 300 Å and dispersion of about 400 Å in the lateral direction.Thus, by modifying the implant energy of the helium PAI, the region ofdopant diffusion may be changed and lateral straggle may be controlled.Similar result may be achieved using a beam line system by modifying thevoltage applied to the extraction electrodes.

FIGS. 9A-9E illustrate lateral straggle control when germanium is usedto perform the PAI. A germanium PAI is illustrated in FIGS. 9A-9C and aboron PAI is illustrated in FIGS. 9D-9E. At higher energies, as shown inFIGS. 9B-9C, the germanium PAI does not allow lateral straggle to becontrolled. This is because germanium is much heavier than helium andthus, implants deep into the substrate rather than dispersing quicklylike a helium PAI. Note that even at 20 KeV, germanium does not have thelateral straggle seen in helium at much lower energy levels. FIGS. 9D-9Eshow that boron, which is lighter than germanium, does not penetrate asdeeply as germanium. However, the increased implant energy does littleto affect the lateral straggle, while it does increase the junctiondepth.

FIGS. 10A-10D are cross-sectional views of a semiconductor deviceshowing the method used to improve lateral straggle. In FIG. 10A, a 250VHe PAI is performed, as was described with respect to FIG. 8A. However,this energy level does not result in enough lateral straggle because theamorphous-crystalline interface is not fully under the sidewall spacer700. Thus, the dopant likely would not fully diffuse under the sidewallspacer and overlap capacitance could occur. A higher implant energy,such as 1000V is illustrated in FIG. 10B and shows improved lateralstraggle. The boron in this instance will diffuse to theamorphous-crystalline interface represented by the dotted line of FIG.10C. This He PAI will result in the ideal dopant profile shown in FIG.10D with either an MS anneal or an SPE anneal.

Use of a helium PAI may prevent channeling of a subsequent implantfollowed by a low-angle source drain extension (SDE) implant. Thus, thedopant may be placed at least partly under any sidewall spacers. Thehelium PAI also may overcome any problems with lateral diffusion thatare caused by a MS anneal or SPE anneal. In the plasma doping system100, ramp voltage, pressure, or other parameters may be configured tocontrol lateral diffusion.

Variations in the implant voltage of the helium PAI may increase lateralstraggle and, consequently, lateral amorphization under the sidewallspacer, or any other obstruction, such as photomask material. Boron,carborane, arsenic, phosphorus or other implanted ions, will diffuse tothis amorphous-crystalline interface at the desired location during ananneal to achieve an optimal active dopant profile. Furthermore, theimplant energy and the dose rate of the helium PAI may be configured toadjust the amorphous-crystalline interface that determines the implantedion junction depth during an anneal. The ability of helium to stop borondiffusion at this interface may allow tailoring of a USJ.

An embodiment of the method described herein is not solely limited toplacing a dopant under a sidewall spacer. Rather, it may be applied toother doping methods. For example, applications where precise junctiondepth or extensive or precise lateral diffusion is required may benefitfrom an embodiment of the process described herein. By varying theimplant energy and the dose rate of the helium PAI, both the lateralstraggle and the junction depth can be controlled.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

1. A method of implanting ions in a workpiece, said ions creating animplanted region having a specific junction depth and extending beneathan obstruction, comprising: determining a width of said obstruction;determining an implant voltage and dose rate needed to a lateralstraggle equal to said width while maintaining said specific junctiondepth; performing a helium pre-amorphizing implant (PAI) at said implantvoltage and said dose rate; and implanting ions, following said heliumPAI, which diffuse under said obstruction to said specific junctiondepth.
 2. The method of claim 1, wherein said obstruction comprises asidewall.
 3. The method of claim 1, wherein said obstruction comprises aphotomask.
 4. The method of claim 1, wherein said helium PAI and saidimplanting are performed using a plasma processing system.
 5. The methodof claim 4, wherein said plasma processing system comprises a platen onwhich said workpiece is placed and wherein said implant voltage isdetermined by a bias voltage applied to said platen.
 6. The method ofclaim 4, wherein said plasma processing system comprises an antenna tocreate a plasma, and said dose rate is determined based on a powersupplied to said antenna.
 7. The method of claim 4, wherein said plasmaprocessing system comprises a platen on which said workpiece is placedand wherein said dose rate is determined by a duty cycle of a biasvoltage applied to said platen.
 8. The method of claim 1, wherein saidhelium PAI and said implanting are performed using a beamline system. 9.The method of claim 8, wherein said buntline system comprises a ionsource and at least one extraction electrode, and wherein said implantvoltage is determined by a voltage applied to said extraction electrode.